Brake noise with summer wheels but not winter ones

[xBa380]

Last Fall I replaced my brakes and rotors with Hawk HPS pads and Powerslot rotors... Used this combo on my girlfriends car before and loved the combo, so stuck with the same for my xB.

They are noise-free, except from about 1mph to 0... They always let out a little chirp or squeal every single time when the car completely stops. Completely quiet otherwise.

Through winter I had my winter wheels on (stock steelies, 16" wheels with snow tires mounted) and noticed the noise went away. I thought maybe the pads/rotors finally completely seated with each other or something... Until today.

Put my summer wheels back on, which are 17" versus the OEM 16". The noise came back again.

So what causes a noise from one wheel to another? I find it so strange! I personally don't mind it that much and honestly I find it quiet humorous, but I am still curious what causes this noise on my 17" wheels, but not my winter steelies?

 

[Quattro Pete]

Originally Posted By: xBa380
They are noise-free, except from about 1mph to 0... They always let out a little chirp or squeal every single time when the car completely stops. Completely quiet otherwise.

I don't know what the answers is, but I just wanted to note that the brakes on my 530i do it, too, regardless which wheels (summer or winter) I have on. It's more of a scrape type sound though rather than squeal. I'm assuming it's my pads.

 

[bdcardinal]

What is the weight difference between the wheel and tire combos?

 

[xBa380]

You know I am not exactly sure, but the winter wheel/tire combo is heavier if I remember correctly, although not sure by how much... I *almost* weighed them today too... But the winter sets do feel heavier when I move them around. Aluminum vs. steel, tire itself is heavier, etc...

 

[SteveSRT8]

resonant frequencies will be different. But that's not a problem we have down south as we don't have but one season.

Personally all I've ever heard about Hawk always had a squeal or two in there...

 

[oldhp]

Maybe the aluminum wheels dissipate heat more???

 

[eljefino]

Originally Posted By: SteveSRT8
resonant frequencies will be different.


+1

 

[xBa380]

Even when the rotors/brakes are stone cold in winter... The winter wheels never made a chirp... The summer ones always do!


As far as the resonant frequencies, what would be resonating? The rotor? The wheel itself?

Does it change because the wheel and rotor become 'one' when bolted together? I have taken vibrations and understand mass relationships with vibrations and everything, just trying to figure out what would be going on in this case exactly though.

 

[oldhp]

Brake squeel is pads vibrating on the rotor face.

 

[xBa380]

Yes, but would that change if a different wheel is mounted to the rotor? Seems like that would be constant and do the same regardless. But I don't know

 

[Brybo86]

Check lug nut torque settings?

 

[Trav]

I bet the steel wheels cover most of the rotor and dont have many holes or slots to let the noise through.
The aluminum summer wheels are probably an open design that let the sound through so you hear the slots making normal noise.

If this is not the case so much for this post.

 

[xBa380]

Trav, you would be correct there. The steel wheels cover more of the rotor than the summer ones. Also, the summer wheels are open-spoke design, where the winter ones are just solid steelies.

But as loud as they chirp/squeal, I would think I would hear it with either wheel. But who knows haha

 

[Trav]

The noise is still there for sure its just where you are positioned in the car is making harder to hear.
I am doing an engine now with a bad piston pin, from inside the car you can hear the double rap loud and clear but under the hood nothing unless you get down near the drivers side wheel well.

Go through a drive up window and let the sound resonate of the walls right next to you and you will noises you never heard before.

 

[eljefino]

Originally Posted By: Trav


Go through a drive up window and let the sound resonate of the walls right next to you and you will noises you never heard before.



Yup and the inside of the aluminum rim must be the perfect "bell" to reflect and amplify the brake noise. It's not itself "active" acoustically, not being phyiscally vibrated by the brakes, but it's there and the right physical size and shape to reflect the sound around.

Though I like the theory that the holes in the rim are acting like a bandpass filter etc.